An Automation Method for Optimizing and Controlling a Reciprocating Compressor Using Load Step, Speed & Suction Pressure Control
Modern PLCs offer the computing power necessary to implement complex control strategies that can incorporate multi-unit supervisory station control as well as individual unit control methodologies based on load and/or flow. When controlling a reciprocating compressor, it is critical that the PLC is able to model unit loads and flows, select stage and optimum load steps, handle curve-crossings, and stay out of operating areas that can lead to serious issues such as rod loads, pin non-reversals, low volumetric efficiencies, high discharge temperatures, and blow through. When properly implemented, these strategies can help maximize the desired performance criteria (flow, fuel, emissions, safety, etc.), while protecting the unit from exceeding its design limits. However, when not implemented properly, a unit under automated control can experience problems that can result in unstable control, and/or a reduction of unit availability. This paper details methodologies for controlling reciprocating compressors using either PD-based approaches or deadband-based approaches. Various issues typically experienced with controlling reciprocating compressors are discussed and possible solutions detailed. Moreover, general control code and flow charts are presented that cover how to effectively control most natural gas services (production, gathering, pipeline, storage, and injection/withdrawal).